1. Field of the Invention
The present invention relates to a starting device for discharge lamp, particularly suitable to a lamp lighting device for vehicle headlights.
2. Brief Description of the Prior Art
The Lamp lighting device for vehicle headlights having a starting transformer equipped with a core is now widely used. In order to avoid an electric current saturation phenomenon that sometimes occurs in the starting transformer equipped with the above-mentioned core, a volume of the core has to be increased. In other words, inductance value in the ordinary transformer, usually equipped with the core, reaches a saturated value (corresponding to the inductance value of a core-less transformer), at a certain electric current value, as shown in FIG. 11 where inductance characteristic curves against electric current value are depicted.
Magnetic properties of the core are influenced by ambient temperature. FIG. 12 depicts relations between initial permeability (xcexci) of A type and B type cores used at a relatively lower temperature (below 100xc2x0 C.) and at a relatively higher temperature (below 150xc2x0 C.) respectively, and temperature T (xc2x0C.) so as to determine Curie temperatures in the respective core types.
The Curie temperature of A type is 174xc2x0 C. for a lower temperature use and that of B type is 200xc2x0 C. for a higher temperature use. Since a ferrite core has a critical temperature (Curie temperature) where the core transforms from ferromagnetic to paramagnetic, the ferrite core with the higher Curie temperature should be used at a higher temperature range (100xc2x0 C.xcx9c200xc2x0 C.).
When an HID lamp is employed as the discharge lamp, the core with Curie temperature above 200xc2x0 C. should be selected for the starting transformer from a safety point, since heat from the lamp raises the temperature of the core up to ca. 150xc2x0 C. when a starting circuit is arranged in a lamp socket due to a short distance between the lamp and the core. The higher Curie temperature of the core is, the lower an initial permeability (xcexci) of the core is (i.e. a lower inductance value when coil turns are kept constant), which means lower performance. Usually such core is not employed so that quantity of the commercially manufactured core is few, which naturally results in a cost increase.
When ferrite type cores are molded by an epoxy resin etc. for insulation, fatal defects such as ruptures or cracks are sometimes formed due to a shrinkage difference between the core and the molded resin. In order to avoid the above-mentioned defects caused by the shrinkage of the molded resin, the core has to be closed in a bobbin etc. or the core with a simple shape (round or rectangular rod etc.) has to be employed.
When a power is applied to the main body (not shown) of the lamp lighting device without mounting the lamp into a socket of the starting device for the discharge lamp, in the worst situations firing or fuming occurs likely due to a high voltage between two electrodes in the socket. Operators also likely suffer from electrical shocks when they fix the lamp lighting devices. As measures against the above-mentioned problems, check terminals etc. (terminals to detect mounting status of the HID lamp) as shown in FIG. 17, disclosed in the Japanese laid open patent No.10-50436, are attached to the lamp lighting devices
In the conventional starting device for discharge lamp with the above-mentioned core, a supporting point of the core was easily broken by vibrations and impacts etc. because of a core weight. As measures against such breakage a core supporting mechanism was reinforced or other supporting members were added. Which resulted in a manufacturing cost increase.
In order to judge whether the HID lamp was mounted or not, additional detecting terminals, except existing two electrode terminals, had to be arranged in the socket, and a circuit (not shown) to process signals from the detecting terminals had to be added to the lamp lighting device.
The present invention is carried out in view of the above-mentioned problems so as to provide an inexpensively constituted, small sized and light weighed device free from breakage due to vibrations and impacts. The device attains electrical and structural connections simultaneously between high voltage electrodes and coils equipped in a starting transformer. And the present invention also provides a starting device for discharge lamp having a function where a power is supplied only when the lamp is mounted.
The starting device for discharge lamp is constituted as follows:
(1) The starting device for discharge lamp comprising; a socket equipped with a high voltage electrode and a grounding electrode for mounting the discharge lamp, a bobbin and a starting transformer having a core-less structure equipped with a primary and a secondary coils wound around the bobbin; wherein a screw electrode is arranged at the center of one end face of the bobbin, one end of the screw electrode is connected to an output terminal of the high voltage side of the secondary coil on the starting transformer and the other end of the screw electrode is screwed so as to be connected to a terminal of the high voltage side of the socket.
(2) The starting device for discharge lamp comprising; a socket for mounting the discharge lamp equipped with a high voltage electrode fitted to a movable electrode holder moved by a spring member and equipped with a grounding electrode for mounting the discharge lamp, a bobbin and a starting transformer having a core-less structure equipped with a primary and secondary coils wound around a bobbin; wherein an insulating wall is protruded by a spring mechanism when a discharge lamp is not mounted between a terminal of the high voltage side of the secondary coil and a grounding terminal; and the insulating wall is accommodated in a space at the center of the bobbin of the starting transformer when the discharge lamp is mounted.
(3) The starting device for discharge lamp according to (1) where the device is equipped with a harness with connector.
(4) The starting device for discharge lamp according to (2) where the device is equipped with a harness with connector.